Hair treatment composition

ABSTRACT

A rinse-off hair treatment composition for improved delivery of amino-acid to the hair and/or scalp comprising:(a) a particulate metal-amino acid complex;(b) at least one surfactant; and(c) a deposition aid.

This application is a division of Ser. No. 08/959,863 filed Oct. 29,1997, now U.S. Pat. No. 5,911,978.

FIELD OF THE INVENTION

This invention relates to hair treatment compositions, and moreparticularly to hair treatment compositions formulated to be rinsed fromthe scalp after application and which contain amino acid actives tomodify or nourish the hair or hair root.

BACKGROUND AND PRIOR ART

Amino acids are known to be important for the nourishment of the humanhair root and the growth of human hair. For example, keratinhydrolysates, a source of amino acids in both free and peptide form, area common ingredient of hair shampoos and the like. Numerous publicationsdescribe the use of an array of amino acids in lotions or tonics fortopical application to cure baldness and other skin, scalp and hairdisorders.

However, to achieve efficacy from rinse-off hair treatment formulationsit is necessary to deliver active ingredients to the site of action, andthe benefits attainable are frequently limited for substances such asamino acids, since a large proportion tends to be removed during therinse stage.

Conventional approaches to this problem have entailed increasingapplication time, and increasing concentration of the active ingredientin the formulation. For example, Franz et al, Fundam.Appl.Toxicol. 21(1993) 213-221 demonstrates different rank orders for penetration fromvarious generic prototype personal products formulations as a functionof the applied dose. This is not feasible under normal in-useconditions, and can result in barrier damage through prolonged contacttime.

There is therefore a need for a rinse-off hair treatment provingenhanced delivery of amino acid.

Metal-amino acid complexes are known and available as such from theprior art. There is a body of literature describing the complexes as away to administer metals as dietary supplements in a non-toxic way toanimals. The amino acid is there to reduce the toxicology profile ofheavy metals. In the personal care area, metal-amino acid complexes havebeen used in hair colouring compositions (Cu or Zn cysteinate, U.S. Pat.No. 4 173,453), antipruritic drugs (zinc-aminoacid conjugates,WO92/10178), and anti-inflammatory creams (SU 1382477). However improveddeposition/substantivity of the amino acid portion in a topicalformulation is not discussed. GB 937,362 describes compositions for thecare and growth of skin, hair and nails containing one or more magnesiumcompounds of an alpha-aminoacid. The acid residue is described as acarrier for the specific introduction of magnesium into the skin andhair cells. U.S. Pat. No. 4,652,445 describes a no-rinse hairconditioner product with the addition of “zinc-releasing ingredients” tosupplement the hair fibre with zinc. The zinc-releasing chemicals may bezinc amino acid complexes, but are preferably zinc-protein orzinc-keratin.

It has now been found that enhanced deposition of amino acid from arinse-off hair treatment composition can be achieved by incorporation ofthe amino acid into the composition as a complex with a metal ion. Thisoffers a performance and cost advantage through improved delivery of theamino acid nutrient to the target substrate, ie hair and/or scalp, perunit dose.

SUMMARY OF THE INVENTION

In one aspect the present invention provides a rinse-off hair treatmentcomposition for improved delivery of amino-acid to the hair and/or scalpcomprising:

(a) a particulate metal-amino acid complex;

(b) at least one surfactant; and

(c) a deposition aid.

In a second aspect the invention provides a method of enhancing thedeposition-of an amino acid from a rinse-off hair treatment composition,comprising incorporating the amino acid into the composition in the formof a particulate metal-amino acid complex.

In a third aspect the invention provides the use of a particulatemetal-amino acid complex, for enhancing the deposition of amino acidfrom a rinse-off hair treatment composition.

DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS

Amino Acid

Examples of the amino acid moiety from which the particulate metal-aminoacid complex is derived include:

arginine

aspartic acid

citrulline

cysteine

cystine

cystathionine

glutamic acid

glutamine

glycine

isoleucine

lysine

methionine

ornithine

serine, and

valine.

Particularly preferred are cysteine, arginine, serine, glutamic acid,glutamine, isoleucine, lysine, methionine and valine.

It is also possible to employ derivatives of the amino acids. Examplesinclude where free -NH2 groups of the amino acid are modified by one ormore of the following:

(i) acyl groups, eg N-alkanoyl in which the alkanoyl moiety has an alkylchain length of from 3 to 20 carbon atoms, preferably from 4 to 10, egN-butanoyl, N-hexanoyl, and N-octanoyl;

(ii) ester groups, eg those in which the alkyl group is straight chainand of from 1 to 20 carbon atoms, preferably from 1 to 4 carbon atoms,eg methyl, ethyl and n-propyl;

(iii) amino acid residues; and

(iv) peptide residues comprising from 2 to 8 amino acid residues.

Mixtures of the amino acids or derivatives thereof may also be used. Asingle molecule of metal complex itself may also contain different aminoacids.

Metal Ion

Preferably the metal ion has a valency of at least 2.

Examples of the metal ion from which the particulate metal-amino acidcomplex is derived include Fe, Cu, Ca, Mn, Sn, Ti and Zn. The mostpreferred metal ion is Zn; this is thought to confer damage protectionto the hair.

Mixtures of metal ions may be used. Also, the same molecule of metalcomplex may contain more than one metal ion, which metal ions may be thesame or different.

In highly preferred compositions of the present invention, theparticulate metal-amino acid complex is zinc cysteinate or zincglutamate, or a mixture of the two.

Particle Size

The average particle size of the metal-amino acid complex incompositions of the invention may range from 0.05 to 50 microns. Ourstudies,(using fluorescent microspheres of different sizes as modelparticles, with visualisation of particle deposition on the skin usingconfocal laser scanning microscopy) indicate that particle size doesinfluence the extent and location of deposition, and that a particularlypreferred average particle size range for targeted delivery to the hairfollicles is 3-10 microns.

The amount of particulate metal-amino acid complex incorporated incompositions of the invention is suitably from bout 0.001 to about 10%by weight of the total composition, ore preferably from about 0.1 toabout 5% by weight.

Surfactant

The composition according to the invention comprises at least onesurfactant, preferably chosen from anionic, cationic, nonionic,amphoteric and zwitterionic surfactants, and mixtures thereof.

A particularly preferred hair treatment composition in accordance withthe invention is a shampoo composition in which at least one surfactantprovides a deterging benefit. The deterging surfactant is preferablyselected from anionic, nonionic, amphoteric and zwitterionicsurfactants, and mixtures thereof.

Suitable anionic surfactants include the alkyl sulphates, alkyl ethersulphates, alkaryl sulphonates, alkanoyl isethionates, alkyl succinates,alkyl sulphosuccinates, N-alkoyl sarcosinates, alkyl phosphates, alkylether phosphates, alkyl ether carboxylates, and alpha-olefinsulphonates, especially their sodium, magnesium ammonium and mono-, di-and triethanolamine salts. The alkyl and acyl groups generally containfrom 8 to 18 carbon atoms and may be unsaturated. The alkyl ethersulphates, alkyl ether phosphates and alkyl ether carboxylates maycontain from one to 10 ethylene oxide or propylene oxide units permolecule, and preferably contain 2 to 3 ethylene oxide units permolecule.

Examples of suitable anionic surfactants include sodium oleyl succinate,ammonium lauryl sulphosuccinate, ammonium lauryl sulphate, sodiumdodecylbenzene sulphonate, triethanolamine dodecylbenzene sulphonate,sodium cocoyl isethionate, sodium lauroyl isethionate and sodiumN-lauryl sarcosinate. The most preferred anionic surfactants are sodiumlauryl sulphate, triethanolamine lauryl sulphate, triethanolaminemonolauryl phosphate, sodium lauryl ether sulphate 1EO, 2EO and 3EO,amnonium lauryl sulphate and ammonium lauryl ether sulphate 1EO, 2EO and3EO.

Nonionic surfactants suitable for use in compositions of the inventionmay include condensation products of aliphatic (C8-C18) primary orsecondary linear or branched chain alcohols or phenols with alkyleneoxides, usually ethylene oxide and generally having from 6 to 30ethylene oxide groups. Other suitable nonionics include mono- ordi-alkyl alkanolamides. Example include coco mono- or di-ethanolamideand coco mono-isopropanolamide.

Amphoteric and zwitterionic surfactants suitable for use in compositionsof the invention may include alkyl amine oxides, alkyl betaines, alkylamidopropyl betaines, alkyl sulphobetaines (sultaines), alkylglycinates, alkyl carboxyglycinates, alkyl amphopropionates,alkylamphoglycinates alkyl amidopropyl hydroxysultaines, acyl tauratesand acyl glutamates, wherein the alkyl and acyl groups have from 8 to 19carbon atoms. Examples include lauryl amine oxide, cocodimethylsulphopropyl betaine and preferably lauryl betaine, cocamidopropylbetaine and sodium cocamnhopropionate.

The surfactants are present in shampoo compositions of the invention inan amount of from 0.1 to 50% by weight, preferably from 0.5 to 30% byweight.

Hair treatment compositions in accordance with the invention may alsotake the form of hair conditioning compositions, which preferablycomprise one or more cationic surfactants. The use of cationicsurfactants is especially preferred, because these ingredients arecapable of providing conditioning benefits to hair.

Examples of cationic surfactants include:

quaternary armnonium hydroxides, e.g., tetramethylanmonium hydroxide,alkyltrimethylammonium hydroxides wherein the alkyl group has from about8 to 22 carbon atoms, for example octyltrimethylammonium hydroxide,dodecyltrimethy- ammonium hydroxide, hexadecyltrimethylammoniumhydroxide, cetyltrimethylammonium hydroxide, octyldimethylbenzylammoniumhydroxide, decyldimethyl- benzylanmonium hydroxide,stearyldimethylbenzylammonium hydroxide, didodecyldimethylarmoniumhydroxide, dioctadecyldimethylaimmonium hydroxide, tallowtrimethylanmonium hydroxide, cocotrimethylannonium hydroxide, and thecorresponding salts thereof, e.g., chlorides

Cetylpyridinium hydroxide or salts thereof, e.g., chloride

Quaternium -5

Quaternium -31

Quaternium -18

and mixtures thereof.

In hair conditioning compositions according to the invention, the levelof cationic surfactant is preferably from 0.01 to 10%, more preferably0.05 to 5%, most preferably 0.1 to 2% by weight of the composition.

Deposition Aid

In accordance with the invention, the hair treatment compositioncontains a polymeric water-soluble deposition aid for the particles ofmetal-amino acid complex. By “deposition aid” is meant an agent whichenhances deposition of the particles of metal-amino acid complex on theintended site, i.e., the hair and/or the scalp.

The deposition aid will generally be present at levels of from 0.01 to5%, preferably from about 0.05 to 1%, more preferably from about 0.08%to about 0.5% by weight. The deposition aid may be a homopolymer or beformed from two or more types of monomers. The molecular weight of thepolymer will generally be between 5 000 and 10 000 000, typically atleast 10 000 and preferably in the range 100 000 to about 2 000 000. Thepolymers will have cationic nitrogen containing groups such asquaternary ammonium or protonated amino groups, or a mixture thereof.

The cationic charge density of the deposition aid, which is defined asthe reciprocal of the molecular weight of a monomeric unit of thepolymer containing 1 charge, has been found to need to be at least 0.1meq/g, preferably above 0.8 or higher. The cationic charge densityshould not exceed 4 meq/g, it is preferably less than 3 and morepreferably less than 2 meq/g. The charge density can be measured usingconductimetric analysis and should be within the above limits at thedesired pH of use, which will in general be from about 3 to 9 andpreferably between 4 and 8.

The cationic nitrogen-containing group will generally be present as asubstituent on a fraction of the total monomer units of the depositionaid. Thus when the polymer is not a homopolymer it can contain spacernon-cationic monomer units. Such polymers are described in the CTFACosmetic Ingredient Directory, 3rd edition. The ratio of the cationic tonon-cationic monomer units is selected to give a polymer having acationic charge density in the required range.

Suitable cationic deposition aids include, for example, copolymers ofvinyl monomers having cationic amine or quaternary ammoniumfunctionalities with water soluble spacer monomers such as(meth)acrylamide, alkyl and dialkyl (meth)acrylamides, alkyl(meth)acrylate, vinyl caprolactone and vinyl pyrrolidine. The alkyl anddialkyl substituted monomers preferably have C1-C7 alkyl groups, morepreferably C1-3 alkyl groups. Other suitable spacers include vinylesters, vinyl alcohol, maleic anhydride, propylene glycol and ethyleneglycol.

The cationic amines can be primary, secondary or tertiary amines,depending upon the particular species and the pH of the composition. Ingeneral secondary and tertiary amines, especially tertiary, arepreferred.

Amine substituted vinyl monomers and amines can be polymerized in theamine form and then converted to ammonium by quaternization.

Suitable cationic amino and quaternary ammonium monomers include, forexample, vinyl compounds substituted with dialkyl aminoalkyl acrylate,dialkylamino alkylmethacrylate, monoalkylaminoalkyl acrylate,monoalkylaminoalkyl methacrylate, trialkyl methacryloxyalkyl ammoniumsalt, trialkyl acryloxyalkyl ammonium salt, diallyl quaternary ammoniumsalts, and vinyl quaternary ammonium monomers having cyclic -cationicnitrogen-containing rings such as pyridinium, imidazolium, andquaternized pyrrolidine, e.g., alkyl vinyl imidazolium, alkyl vinylpyridinium, and alkyl vinyl pyrrolidine salts. The alkyl portions ofthese ,monomers are preferably lower alkyls such as the C1-C3 alkyls,more preferably C1 and C2 alkyls.

Suitable amine-substituted vinyl monomers for use herein includedialkylaminoalkyl acrylate, dialkylaminoalkyl methacrylate,dialkylaminoalkyl acrylamide, and dialkylaminoalkyl methacrylamide,wherein the alkyl groups are preferably C1-C7 hydrocarbyls, morepreferably C1-C3, alkyls.

The deposition aid can comprise mixtures of monomer units derived fromamine- and/or quaternary ammonium-substituted monomer and/or compatiblespacer monomers.

Suitable deposition aids include, for example: cationic copolymers of1-vinyl-2-pyrrolidine and 1-vinyl-3-methyl-imidazolium salt (e.g.,Chloride salt) (referred to in the industry by the Cosmetic, Toiletry,and Fragrance Association, “CTFA”. as Polyquaternium-16); copolymers of1-vinyl-2-30 pyrrolidine and dimethylaminoethyl methacrylate (referredto in the industry by CTFA as Polyquaternium-11; cationic diallylquaternary ammonium-containing polymers including, for example,dimethyldiallylammonium chloride homopolymer (referred to in theindustry (CTFA) as Polyquaternium 6); ineral acid salts of amino-alkylesters of homo-and copolymers of unsaturated carboxylic acids havingfrom 3 to 5 carbon atoms, as described in U.S. Pat. No. 4,009,256; andcationic polyacrylamides as described in UK Application No. 9403156.4.

Other cationic deposition aids that can be used include cationic guargum derivatives, such as guar hydroxypropyltrimonium chloride(Commercially available from Celanese Corp. in their Jaguar trademarkseries).

Examples are JAGUAR C13S, which has a low degree of substitution of thecationic groups and high viscosity. JAGUAR C15, having a moderate degreeof substitution and a low viscosity, JAGUAR C17 (high degree ofsubstitution, high viscosity), JAGUAR C16, which is a hydroxypropylatedcationic guar derivative containing a low level of substituent groups aswell as cationic quaternary ammonium groups, and JAGUAR 162 which is ahigh transparency, medium viscosity guar having a low degree ofsubstitution.

Preferably the deposition aid is selected from the group comprisingcationic polyacrylamides, and cationic guar derivatives. Particularlypreferred deposition aids are Jaguar C13S with a cationic charge densityof 0.8 meq/g. Other particularly suitable materials include Jaguar C15,Jaguar C17 and Jaguar C16 and Jaguar C162.

Suspending Agent

The composition may optionally further comprise from 0.1 to 5 % of asuspending agent. Examples are polyacrylic acids, cross linked polymersof acrylic acid, copolymers of acrylic acid with a hydrophobic monomer,copolymers of carboxylic acid-containing monomers and acrylic esters,cross-linked copolymers of acrylic acid and acrylate esters,heteropolysaccharide gums and crystalline long chain acyl derivatives.The long chain acyl derivative is desirably selected from ethyleneglycol stearates, alkanolamides of fatty acids having from 16 to 22carbon atoms and mixtures thereof. Polyacrylic acid is availablecommercially as Carbopol 420, Carbopol 488 or Carbopol 493. Polymers ofacrylic acid cross-linked with a polyfunctional agent may also be used,they are available commercially as Carbopol 910, Carbopol 934, Carbopol940, Carbopol 941 and Carbopol 980. An example of a suitable copolymerof a carboxylic acid containing a monomer and acrylic acid esters isCarbopol 1342. All Carbopol materials are available from Goodrich andCarbopol is a trade mark. A further suitable suspending agent isdihydrogenated tallow phthalic acid amide (available from StepanChemical Co. under the trademark Stepan TAB-2)

Suitable cross linked polymers of acrylic acid and acrylate esters arePemulen TR1 or Pemulen TR2. A suitable heteropolysaccharide gum isxanthan gum, for example that available as Kelzan mu.

Conditioning Agents

Hair treatment compositions of the invention may also optionally containone or more conditioning agents, as are well known in the art. Theconditioning agents may include silicones, protein hydrolysates,quaternised protein hydrolysates, and other materials which are known inthe art as having. desirable hair conditioning properties.

Silicones are the most preferred conditioning agents.

Suitable silicones include volatile and non-volatile silicones, such asfor example polyalkylsiloxanes, polyalkylaryl siloxanes, siloxane gumsand resins, cyclomethicones, aminofunctional silicones, quaternarysilicones and mixtures thereof. Silicone oil is a particularly preferredconditioning agent for hair. The silicone may be in the form of a lowviscosity oil which may contain a high viscosity oil or gum in solution.Alternatively, the high viscosity material may be in the form of anemulsion in water. The emulsion may be of high viscosity oil or of asolution of gum in a lower viscosity oil. The particle size of the oilphase may be anywhere in the range from 30 nanometres to up to 20microns average size.

The silicone oil may suitably be a polydimethylsiloxane with an averageparticle size of less than 20 microns and preferably less than 2microns. Small particle size enables a more uniform distribution ofsilicone conditioning agent for the same concentration of silicone inthe composition. Advantageously, a silicone with a viscosity in therange 1-20 million cst is used. The silicone is preferablyemulsion-polymerised, since this enables silicones of very highviscosity to be more easily processed. The silicone can be cross-linked.

Suitable protein hydrolysates include lauryl dimonium hydroxypropylamino hydrolysed animal protein, available commercially under thetrade name LAMEQUAT L, and hydrolysed keratin containing sulphur-bearingamino acids, available commercially under the trade name CROQUAT WKP.

Fatty Alcohol

Another ingredient that may optionally be incorporated into hairtreatment compositions of the invention is a fatty alcohol material. Theuse of these materials is especially advantageous in conditioningcompositions of the invention, in particular conditioning compositionswhich comprise one or more cationic surfactant materials. The combineduse of fatty alcohol materials and cationic surfactants in conditioningcompositions is believed to be especially advantageous, because thisleads to the formation of a lamellar phase, wherein the cationicsurfactant is dispersed.

Preferred fatty alcohols comprise from 8 to 22 carbon atoms, morepreferably 16 to 20. Examples of preferred fatty alcohols are cetylalcohol and stearyl alcohol. The use of these materials is alsoadvantageous in that they contribute to the overall conditioningproperties of compositions of the invention.

The level of fatty alcohol materials is conveniently from 0.01 to 10%,preferably from 0.1 to 5% by weight of the composition. The weight ratioof cationic surfactant to fatty alcohol is preferably from 10:1 to 1:10,more preferably from 4:1 to 1:8, most preferably from 1:1 to 1:4.

Water

The hair treatment compositions of the invention are preferably aqueousbased. The compositions suitably comprise water in amount of from about20 to about 99% by weight of the total composition.

Method of Use

The compositions of the invention are preferably rinse-off compositions,i.e., suitable for applying to the hair and/or scalp, left thereon foran appropriate period of time and then rinsed off with water. Thus,shampoos are a particularly preferred product form for compositions ofthe invention.

Other Optional Ingredients

Depending on the type of composition employed, one or more additionalingredients conventionally incorporated into hair treatment formulationsmay be included in the compositions of the invention. Such additionalingredients include opacifiers such as polyethylene glycol distearateand ethylene glycol stearates, polymer lattices, additionalantimicrobial agents, foam boosters, perfumes, colouring agents,preservatives, viscosity modifiers, proteins, polymers, buffering or pHadjusting agents, moisturising agents, herb or other plant extracts andother natural ingredients.

BRIEF DESCRIPTION OF DRAWINGS

The invention is further illustrated by way of the followingnon-limitative examples, in which:

FIG. 1 is a graph showing the % dose deposition onto dermatomed pig skinin vitro of cysteine in both free and metal complexed form from ashampoo base.

EXAMPLES

Materials

Radiolabelled and non-radiolabelled cysteine for the synthesis of zinccysteinate was obtained as follows: L-[³⁵S]-cysteine (>1000 Ci/mmol) ina stabilising solution containing potassium acetate, 20 mM, anddithiothreitol, 5 mM, at pH7 was purchased from Amersham InternationalPlc (Little Chalfont, U.K.). L-Cysteine (approx. 98%) was obtained fromSigma Chemical Co. (St Louis, M.o., U.S.A.).

Dulbecco's phosphate buffered saline (10× concentrate) andpenicillin/streptomycin (5000 IU/ml/5000 g/ml) were purchased from Lifetechnologies Ltd (Paisley, U.K.). Anhydrous D-(+)-glucose was obtainedfrom Sherman Chemicals Ltd (Sandy, U.K.). Buffer was prepared withdistilled water.

Methods

1. Synthesis of Zinc Cysteinate

Basic zinc carbonate (10 g) was added to a solution of cysteine in water(14.92 g/100 ml) and was heated under reflux for 16h with stirring. Theoff-white microcrystalline solid was collected by filtration, washedwith water and dried in air. The empirical formula for the complex, asdetermined by thermogravimetric analysis, was; Zn[SCH₂CH(NH₂)CO₂]. Thisempirical formula was confirmed by matching the Fourier transforminfra-red spectrum for the product with a reference spectrum for thiscomplex, Shindo and Brown, J.Am.Chem.Soc. 87 (1965) 1904-1909.

2. Size Reduction of Zinc Cysteinate

2.1 Sonication

Zinc cysteinate suspensions in distilled water (1%w/v) were sonicatedover ice for 5 minutes with a ultrasonic probe at maximumamplitude(Soniprep, MSE, U.K.).

2.2 Laser Light Scattering

Aliquots of sonicated suspension were placed in a Malvern Mastersizer. A300 mm lens with a 3 mm path length cell was connected to the smallsample presentation unit which was stirred continuously. Lightscattering data was analysed using a sample presentation code of 0700.

Cumulative mass distributions were prepared using a computer spreadsheetprogram (Microsoft Excell®). The particle size data quoted, however,were obtained directly from the Mastersizer output.

3. Skin Deposition Studies

3.1 Preparation of Formulations

In order to calculate the equivalent amount of free cysteine for a givenamount of complexed material the following empirical formula for thezinc cysteinate complex was used; Zn[SCH₂CH(NH₂)CO₂], i.e. cysteinemakes up 64.96% of the total formula weight.

Differences in the detection methods used for the free and the complexedcysteine meant that, formulations containing free cysteine includedradiolabelled cysteine, and formulations containing complexed cysteinedid not contain any radiolabel.

Two types of shampoo were prepared for both the free and the conplexedcysteine. One shampoo with a deposition aid, JAGUAR, and one without.The shampos had the following formulations:

% w/w ingredient complexed cysteine free cysteine formulationsformulations with without with without deposition deposition depositiondeposition aid aid aid aid cysteine 1.39 1.38 ‘cysteine 1.38 1.38equivalent’ deposition 0.10 — 0.10 — aid: JAGUAR C13S (guarhydroxypropyl trimonium chloride) sodium 14.00 14.00 14.00 14.00 laurethsulphate cocamido- 2.00 2.00 2.00 2.00 propyl betaine dimethiconol 1.601.60 1.60 1.60 and TEA- dodecyl- benzene sulphonate sodium 0.50 0.500.50 0.50 benzoate Amplitude 484 0.50 0.50 0.50 0.50 glycol 8.00 8.008.00 8.00 distearate (and) laureth-4 (and) cocamido- propyl betainesodium 1.00 1.00 1.00 1.00 chloride citric acid to pH 4.5- to pH 4.5- topH 4.5- to pH 4.5- 5.0 5.0 5.0 5.0 water to 100 to 100 to 100 to 100

In order to mimic in-use conditions as closely as possible, each shampoowas diluted tenfold with water prior to application to the skin. Thistenfold dilution reflects the dilution that occurs when people applyshampoo to wet hair.

For each free cysteine formulation, 45.4 μl of L-[³⁵S]-cysteine (480 μCion the day of preparation), 30 μl of shampoo and 224.6 μl of 0.185%w/vL-cysteine were mixed together in a plastic microcentrifuge tube. Thisproduced 300 μl of 1 in 10 diluted shampoo suitable for dosing over 10diffusion cells; each dose containing 40 μCi L-[³⁵S]-cysteine, having avolume of 25 μl and a cysteine concentration of 138%w/w.

For each complexed cysteine formulation, lml of shampoo was mixed with2.12 ml of 0.212%w/v sonicated zinc cysteinate suspension and 6.88 ml ofwater. This produced 10 ml of 1 in 10 diluted shampoo with an equivalentcysteine concentration of 1.38%w/w. The zinc cysteinate suspension wasprepared using the ultrasonic probe method detailed in 2.1 above. Theparticle size of the size-reduced zinc cysteinate was checked usingLaser Light Scattering (2.2 above). The mass median diameter of thesize-reduced zinc cysteinate was determined to be 8.27 μm. The particlesize distribution was unimodal; 10% of the particles being <2.91 μm indiameter and 90% <22.46 μm.

3.2 Preparation of the Skin

The skin of the back of a two-month-old pig was used. First the skin waswashed with 75% ethanol. This was done in order to remove sebum. Thenthe hairs were clipped off with an electric clipper (Oster, U.S.A.).Subcutaneous fat was scraped away with a post mortem knife (Raymond andLamb). The prepared skin was then stored frozen until use. On the day ofthe experiment, the skin was thawed, dermatomed to a thickness ofapprox. 500 μm (Deca Dermatome, DePuy Healthcare, Leeds, U.K.) and thenfloated on Dubecco's modified phosphate buffered saline (pH7.4containing 0.1% glucose, DMPBS).4

3.3 Skin Deposition Experiments

Diffusion experiments used Teflon® flow-through diffusion cells, (CrownBioscientific Inc, Somerville, N.J., U.S.A.). The cells had a receptorvolume of 130 μl and an exposed surface area of 0.38 cm². Cells weremaintained at a temperature of 37° C. on metal aluminium heating blocks(Posiblock® Diffusion Cell Heater, Crown Glass Co.) heated by acirculating water bath. In this way the skin surface temperature washeld at approximately 32° C.; normal skin surface temperature. Receptorcompartments were filled with DMPBS to maintain good skin hydration.

For each of the four formulations, 25 μl of 1 in 10 diluted formulationwas applied to the skin. The dose volume used was chosen on the basisthat usually 5 g of product is applied to a typical scalp surface-areaof 700 cm², and therefore that the undiluted shampoo dose per unit areais 7.1 mg/cm², and therefore that the dose per 0.38 cm² is approximately2.7 μl. This equates to approximately 25 μl of 1 in 10 diluted product.

Dosing was performed with a 25 μl positive displacement pipette(Anachem, Luton, U.K.). Formulations were applied for 1 minute andrinsed off with 10×0.5 ml of DMPBS. The buffer was applied to the skinusing a 1 ml Gilson pipette and taken off with a disposable pipette. Theskin surface was rinsed three times with each wash by aspirating andreapplying the buffer.

After washing, the skin was left in the diffusion cells for 2 hours.Skin samples were then taken out of each cell and the application areacut from the trimmings with a pair of scissors. In radiolabelexperiments, skin samples were solubilised in 2 ml of 90%v/vSoluene-350® in distilled water. Samples were solubilised overnight at50° C. Solubilised samples were mixed with 16 ml Hionic-Fluor® (PackardInstrument Co.) prior to scintillation counting.

In radiolabel experiments, all samples were counted on a BeckmanLS6000IC liquid scintillation counter (Beckman Instruments, Inc.,Fullerton, Calif., U.S.A.).

3.4 Atomic Absorption Spectroscopy

Blank and treated skin samples (typically 10-20 mg.) were weighed intoscrew-top PTFE liners and 0.25 ml of concentrated nitric acid added. Theliner was capped, placed inside a stainless steel digestion vessel andheated at 140° C. for 2 hours. After cooling the digests were diluted to10 ml. with deionised water.

Tissue digests were analysed by comparison against known standards usingflame atomic absorption spectrometry under the following conditions :air/acetylene flame, wavelength=213 nm, slit width=0.7 nm.

Results

A summary of skin deposition data is shown below in Table 1. Valuesrepresent means of 8-10 replicates. Values in brackets represent 2×standard error.

TABLE 1 % dose deposited without JAGUAR with JAGUAR free cysteine 0.51(0.26) 0.83 (0.31) zinc 1.81 (0.98) 4.85 (1.81) cysteinate

Conclusions

Statistical analysis revealed that for both zinc cysteinate treatments,zinc levels in the skin samples as measured by atomic absorptionspectroscopy were significantly greater than blank skin values (P<0.05,Student's T-test, equal variances). Furthermore, zinc cysteinatedeposition was significantly improved by inclusion of the Jaguardeposition aid (P<0.05, Student's T-test, equal variances). As expected,Jaguar had no effect on the deposition of the free cysteine (P<0.05,Student's T-test, equal variances).

What is claimed is:
 1. A rinse-off hair treatment composition forimproved delivery of amino-acid to the hair and/or scalp comprising: (a)a particulate metal-amino acid complex; (b) at least one surfactant; and(c) a polymeric, water-soluble deposition aid.
 2. A compositionaccording to claim 1, in which the metal ion has a valency of at least2.
 3. A composition according to claim 1 or 2, in which the amino acidis selected from the group consisting of cysteine, arginine, serine,glutamic acid, glutamine, isoleucine, lysine, methionine valine, andmixtures thereof.
 4. A composition according to any of claims 1 to 3 inwhich the particulate metal-amino acid complex is zinc cysteinate orzinc glutamate, or a mixture of the two.
 5. A composition according toany preceding claim, in which the average particle size of theparticulate metal amino-acid complex is from 3-10 microns.
 6. Acomposition according to any preceding claim which is a shampoocomposition comprising from 0.5 to 30% by weight of a detergingsurfactant selected from anionic, nonionic, amphoteric and zwitterionicsurfactants, and mixtures thereof.
 7. A composition according to anypreceding claim in which the deposition aid is selected from the groupconsisting of cationic polyacrylamides, and cationic guar derivatives.8. A method of enhancing the deposition of an amino acid from arinse-off hair treatment composition, to the hair comprisingincorporating the amino acid into the composition in the form of aparticulate metal-amino acid complex.
 9. A composition in accordancewith claim 1, wherein said deposition aid is to enhance deposition ofparticles of said metal-amino acid complex on the hair and wherein saiddeposition aid is a homopolymer with a molecular weight between 5,000and 10,000,000, and wherein said homopolymer has cationic nitrogencontaining groups, and wherein the cationic charge density of thedeposition aid is at least 0.1 milli-equivalents per gram to 4milli-equivalents per gram.
 10. A composition according to claim 1,wherein said deposition aid is a copolymer containing spacernon-cationic monomer units and said copolymer is of vinyl monomersselected from the group consisting of acrylamide, methacrylamide, alkyland dialkyl acrylamides, alkyl and dialkyl methacrylamides, alkylacrylates, alkyl methacrylates, vinyl caprolactone and vinylpyrrolidine.
 11. A deposition aid in accordance with claim 9, whereinsaid cationic amines can be primary, secondary or tertiary amines.
 12. Acomposition according to claim 1, wherein said deposition aid is guarhydroxypropyltrimonium chloride.